1. Field of the Invention
The present invention relates to exposure apparatuses, exposure methods, and device manufacturing methods, and more particularly to an exposure apparatus and an exposure method which are used in a lithography process to produce electronic devices such as a semiconductor device and the like, and a device manufacturing method which uses the exposure apparatus or the exposure method.
2. Description of the Background Art
Conventionally, in a lithography process for manufacturing electron devices (microdevices) such as semiconductor devices (such as integrated circuits) and liquid crystal display devices, exposure apparatuses such as a projection exposure apparatus by a step-and-repeat method (a so-called stepper) and a projection exposure apparatus by a step-and-scan method (a so-called scanning stepper (which is also called a scanner) are mainly used.
Substrates such as a wafer, a glass plate or the like subject to exposure which are used in these types of exposure apparatuses are gradually (for example, in the case of a wafer, in every ten years) becoming larger. Although a 300-mm wafer which has a diameter of 300 mm is currently the mainstream, the coming of age of a 450 mm wafer which has a diameter of 450 mm looms near. When the transition to 450 mm wafers occurs, the number of dies (chips) output from a single wafer becomes double or more the number of chips from the current 300 mm wafer, which contributes to reducing the cost. In addition, it is expected that through efficient use of energy, water, and other resources, cost of all resource use will be reduced.
Semiconductor devices are gradually becoming finer, therefore, high resolution is required in exposure apparatuses. As means for improving the resolution, shortening a wavelength of an exposure light, as well as increasing (a higher NA) a numerical aperture of a projection optical system can be considered. To increase the substantial numerical aperture of the projection optical system as much as possible, various proposals are made of a liquid immersion exposure apparatus that exposes a wafer via a projection optical system and liquid (refer to, e.g., U.S. Patent Application Publication 2005/0259234, U.S. Patent Application Publication 2008/0088843 and the like).
However, in the local liquid immersion type exposure apparatuses disclosed in, for example, U.S. Patent Application Publication 2005/0259234, U.S. Patent Application Publication 2008/0088843 and the like, in the case of constantly maintaining a liquid immersion space formed under the projection optical system so as to maximize throughput, a plurality of stages (for example, two wafer stages, or a wafer stage and a measurement stage) has to be placed right under the projection optical system interchangeably.
When the size of the wafer becomes as large as 450 mm, while the number of dies (chips) output from a single wafer increases, a risk also occurs of throughput deceasing due to an increase in the time required to perform an exposure process on a single wafer. Therefore, as a method of improving throughput, employing a twin stage method can be considered where an exposure process on a wafer is performed on one wafer stage, and processing such as wafer exchange, alignment or the like is performed concurrently on another wafer stage, as is disclosed in, for example, U.S. Pat. No. 6,590,634, U.S. Pat. No. 5,969,441, or U.S. Pat. No. 6,208,407 and the like. However, applying the exposure apparatus using the conventional twin stage method to the processing of the 450 mm wafer increased the size of the wafer stage, as well as its weight, which could decrease the position controllability, and consequently decrease an overlay accuracy between a pattern (shot area) already formed on a wafer and a pattern of the next layer.